The invention relates to a hair curling roller adapted to be heated before being placed into the hair. It relates more particularly to a cylindrical hair curling roller comprising a hollow metal core and an outer plastic shell provided with a plurality of outwardly projecting teeth or pins.
Hair curling rollers are substantially cylindrical in shape and are being used by wrapping strands of hair around their periphery to shape the hair in curls or waves, with the curl or wave diameter corresponding to the outer diameter of the roller.
In order to achieve a curl that will last a reasonable length of time the hair strands should be heated while they are wrapped around the roller and should not be removed from the roller until they have cooled down.
Most rollers available are being preheated before being applied to the hair by being placed on a series of metal posts which are being heated electrically, and the temperature of which is regulated by means of a thermostat.
The conventional hair roller comprises a molded plastic cylindrical shell with integrally molded radial teeth or pins on its periphery and a metal sleeve inserted therein. The teeth or pins serve a dual purpose: they grip the hair and pull it tightly against the cylindrical surface; and the tips of the teeth remain substantially cooler than the cylinder body so that the user can touch the hot roller without burning his fingertips; in addition, the teeth keep the hot roller away from the user's head, neck or ears.
The metal sleeve is close to the heated metal post of the heating set and transfers the heat to the plastic shell, the sleeve being instrumental in equalizing the surface temperature of the roller over its entire surface. In some embodiments the rollers are equipped with an inner walled metal sleeve containing paraffin wax with the object of maintaining the temperature for a longer period, and there are some rollers without any insert at all.
The common drawback of all types of molded plastic rollers is caused by the low thermal conductivity of plastic--polypropylene, for example, has a thermal conductivity of 0.04-0.06 BTY/HR, FT, .degree. F., compared with Aluminum which has a conductivity of 128 BTU, HR, FT, .degree. F.--which means that: (a) the roller will take a long time to reach its desired outer surface temperature;
(b) When the hot roller touches the cold hair its outer surface will instantly cool down, as heat is extracted from the surface faster than it can be restored by heat flow from the body of the roller, and (c) as heat conducts slowly through the plastic medium the roller will take a long time to cool down along with the hair surrounding it, thus requiring the user to keep the rollers in the hair a long time out of fear that the warm hair would not retain the curl, after the still warm roller has been removed. It is obvious that all 3 problems would be alleviated if the roller was made of aluminum.
The present invention has, therefore, been conceived with the following objects in mind:
(1) To provide a hair roller which can be rapidly heated while being placed on the post of a heating set, which will impart its heat instantly to the hair wrapped around it and which will cool off rapidly after its heat has been absorbed by the hair.
(2) To provide such hair roller with plastic teeth which will not reach the temperature of the main body and will remain cool enough to be held by the user's fingers.